The prior-art technique for manufacturing kitchen fittings and, to some extent, also furniture products is to a considerable extent based on the use of particle board. The particle board products have appeared to be competitive by the relatively low price and suitability of the material for constructing geometrically simple configurations.
However, there are drawbacks of technical rather than economic nature, which in some cases are very annoying. The liberty in designing is highly restricted by the standard particle boards being made planar only and in large dimensions, which during manufacture are made into components which are planar as well. Besides, the particle board is brittle during drilling and edge processing, and instead of gluing, a special mechanical technique must be used for joining. Moreover, the dimensional stability and the resistance to moisture are unsatisfactory. Recently, the attention paid to the content of formaldehyde in the adhesive used in the particle board has pointed to the shortcoming of the particle board when requiring increased consideration of the environment and harmony with the ever increasing preference of the market for ecologically adapted products.
A substitute for particle boards which would permit that constructions, kitchen fittings and other interior fittings could be manufactured while taking greater liberty in aesthetical and designing respects, could be manufactured in a simpler way and at lower cost than the present technique and could be environmentally adapted to the market's wishes if full freedom from formaldehyde and other environmentally questionable chemicals would be of great interest to the industry manufacturing wooden articles.
Also for the construction and manufacture of dimensionally and moisture stable building products, fittings in cars and other vehicles, appliance enclosures, returnable packages etc., an ecological cellulose-based material permitting simple compression molding would be of interest to the market and be correct in these days.
The new chemically modified cellulose-based product according to the present invention has surprisingly been found to render the above possible. This is achieved by a specific combination of esterification of the hydroxy groups included in the material with a dicarboxylic acid anhydride, and treatment with a polyol, wherein the choice of the used reactants and especially their mutual quantities and how the chemical modification is carried out have been found to result in a product having good physical and chemical properties, which, as stated above, in many respects can be resembled to a plastics granulate in the respect that the inventive product functions as an intermediate product which is stable in storage and which can be formed by the final user quite separately from the original place of manufacture.
Before the invention is described in greater detail, it may be added in this context that the technique of esterifying the cellulose in wood with a dicarboxylic acid anhydride is per se known, for instance from Wood Sci.Technol. 22:21-32 (1988). The wood products described therein are, however, cross-linked with diallyl glycidyl ether which is very reactive and is obviously reacted with the remaining components fairly instantaneously. Therefore, the system can only be used in a conventional plant for making particle boards, i.e. the particle boards are pressed in immediate and direct connection with the chemically modified wood product. Moreover, according to this publication, a catalyst in the form of dicumyl peroxide is required, which yields a final product which is red or golden brown and has an unpleasant smell. Finally, it may be noted that allyl glycidyl ether is an expensive chemical, which is probably one of the reasons why this technique has not come into practical use, especially since the allyl glycidyl ether is used in an essentially greater amount than in the product according to the present invention.
The combination of maleic anhydride and glycerol is also known per se in connection with wood from the publication H. Fujimoto, K. Yamagishi, Chemical Treatment of Wood with a Maleic Acid and Glycerol Mixture. International Symposium on Chemical Modification of Wood, May 17-88, 1991, Kyoto, Japan. In this case, it is, however, a matter of reducing the swell of the wood when contacting water, the treatment being carried out with an aqueous solution of maleic anhydride and glycerol. In other words, maleic anhydride and glycerol are first allowed to react with one another, which occurs at about 100.degree. C., whereupon the mixture is dissolved in water and sprayed onto the wood product. When manufacturing particle boards, particles are then sprayed with said solution, whereupon gluing with a phenol-formaldehyde adhesive and pressing are carried out in conventional manner. Although in this case a low thickness swell is obtained in connection with immersion in water, the disadvantages of the method are that the preparation of the mixture is carried out separately, that the product contains water which makes pressing difficult (vapor forms and may delaminate the particle product), and that the product must be glued with a formaldehyde-containing adhesive like in conventional particle board manufacture. An intermediate product which is stable in storage is therefore not obtained in this case either.